The invention concerns the cutting of the leader of the web in a paper or board machine in the drying section of said machine and in cylinder drying sections of on-machine coating machines. At present, for said purpose, a revolving toothed circular blade (circular saw) is used, in which case the paper web must be separated from the drying wire at the cutting point in order that the blade should not cut the drying wire as well.
A second mode is cutting of the web that has been separated from the drying wire by means of a high-pressure water jet (P&gt;400 bar). The required pressure is high, because, with lower pressures, the web that is not supported against the drying wire at the cutting point is torn irregularly, which results in web breaks.
In many paper and board machines, the cutting of the leader of the web is carried out at the so-called wet end of the machine on the Fourdrinier wire or below the so-called pick-up felt in the press section. In said cutting processes, the dry solids content of the web placed on the Fourdrinier wire is about 10 . . . 20%, commonly about 15%. The strength of such a wet web is very low, and it can be cut readily. In the cutting performed in the wet end of a paper and board machine, it is possible to use low pressures in the diagonal cutting. The pressure values are, as a rule, about 10 . . . 20 bar, more commonly about 12 . . . 14 bar.
At the end of the drying section, the dry solids content of the web is about 90 . . . 98%, most commonly about 94 . . . 95%. After the drying section of a coater, the dry solids content is commonly about 96 . . . 98%. The strength of such a web is far higher than the strength of a web whose dry solids content is about 20% or less, the latter sort of web being usually cut by means of a water jet.
The method has incontestable advantages over the methods that are used currently. It does not produce cutting dust in the air, which dust is detrimental when it adheres to the paper web and to the equipment in the paper mill. The devices in accordance with the method of the invention are simple and durable, and they require little maintenance. The cutting process does not increase the noise level in the premises to a significant extent. The web is not torn irregularly, nor is it broken because of the cutting, which is of great importance. In the cutting in accordance with the method, the web is not separated from the drying wire, which simplifies and improves the transfer of the web, which results in an improved efficiency in the time of utilization of the machine.